IB makeover..........

[Sonnie]

Show off!

[Rodny Alvarez]

This is weird or interesting, I remove the side panels from the boxes so I can do the acoustic material and I decided to run a sweep just to see what it will do.........................check this out...................:holycow:

NO EQ
I'm late to work...........

[Sonnie]

Yeah... that doesn't look too good really. You take a serious hit from about 9Hz to 17hz and some ugliness from 30Hz to 45Hz. Of course you do gain something from 5Hz to 7hz... for whatever it might be worth.

[brucek]

you do gain something from 5Hz to 7hz

Probably not. That would be the rising plot situation we talked about sonnie, caused by the mic calibartion file compensating for a signal in the noise.

Those two plots are correctly responding to the situation.

The gold line is acting like a proper vented system. As the frequency approaches the tune, the output rises and then drops off quickly below the tune. You've gained where it's important.

Without the vented port, the green line represents an IB again and drops down at 15Hz.

I think both plots are enjoying room gain, although I don't really put much faith in any plot line below about 10Hz.

brucek

[Sonnie]

Yeah... below 10Hz does indeed sound almost meaningless.

[Rodny Alvarez]

The IB without the port started to drop at 18Hz and now with the port it goes all the way down............... I was just playing around!!.
Another thing is the you can hear the BIG difference on how much louder the SLLT plays!!, turn the gain all the way up with the IB and it didn't came close to the SLLT.
Finish the flares and didn't make any difference


Now I need to move the tiles

[WillyD]

Yeah, didn't expect the flares to really make a noticeable difference. You most likely never came close to port noise in the first place. Are you gonna take new measurements now though?

[Rodny Alvarez]

I will tomorrow!!
there is little port noise... when I played 10Hz, but the only way to hear it is getting about a foot from the port, when I'm in the listening position cant hear anything!!

[SteveCallas]

The tune probably dropped a bit, but it won't be noticable except in measurements. With something like a 3" or 4" port for a sub, flaring is critical - with a 10" port, not so much But it looks great and matches the rest of the sub system.

The naked VR3 is sexy too

[collo]

Hi Rodny,

I'm interested in your observations on the port noise. You may or may not know that I've done a fair bit of work on the subject. The rig I used only allowed me to test ports up to 6 inches, and frequencies down to 20hz.

Your observations would add quite a bit of value to that work if you could do a small test or two.....


Do you think you could repeat the situation that produced the 10 hz chuffing at close range, whilst measuring the voltage across the driver?

From the voltage and the DC resistance of the driver, the input power can be modelled:

Input power = RMS voltage squared / DC resistance of coil

Plugging this power into WinISD allows the velocity at the test frequency to be read off.

If you could let me know this velocity, along with the actual ID of the port, and the flare radius, it would allow me to increase the accuracy of the "flare-it" software for large ports.

I know SteveC uses this software, as do many others. With the popularity of some of the larger sonosubs, an 8 inch port is sometimes employed, and it would be nice to have a frame of reference that is derived from a large port such as yours.

If you were able to do a second test at 20 or 25hz, this would extend the accuracy even further. (you may not be able to generate enough airflow for the ports to misbehave at these frequencies)

thanks
Collo

[Rodny Alvarez]

SteveCallas wrote:

The naked VR3 is sexy too

Very...........very sexy indeed!!!

Do you think you could repeat the situation that produced the 10 hz chuffing at close range, whilst measuring the voltage across the driver?

I used the REW!
Measure AC or DC voltage???
At the driver or can I do it at the amp??
Remember I have two subs on each box, so were do you want me to measure or does it matter?
What volume or spl??

Input power = RMS voltage squared / DC resistance of coil

[Rodny Alvarez]

The two FRs..........with and w/o flares and mains.
You can see a little difference........


W/flares....

W/o

W/o and mains

[Ilkka]

Rodny,

A small request: when comparing different measurements, put them in the same graph by using the "all measured" tab. It will be much easier to see the little differences then.

[SteveCallas]

Looks like the tuning dropped maybe 0.5hz. Did you add some lining yet or is that still on the to do list? I'd love to hear that system one day.

[Rodny Alvarez]

SteveCallas wrote:

Looks like the tuning dropped maybe 0.5hz. Did you add some lining yet or is that still on the to do list? I'd love to hear that system one day.

I used some 1/2" foam(2 1/2lbs x square foot) and 1" poly-fill, I still need to wrap the port with Dynamat.

Come on down !....... you just need to plan a trip to Alabama, and maybe we can go to Sonnies house

[collo]

Hi again Rodny,

I just had another look at your photos and see that the inside end of the ports is unflared. This would invalidate any test results because any chuffing you hear is probably coming from inside the port.

Thanks anyway
Collo

[Rodny Alvarez]

collo wrote:

Hi again Rodny,

I just had another look at your photos and see that the inside end of the ports is unflared. This would invalidate any test results because any chuffing you hear is probably coming from inside the port.

Thanks anyway
Collo

I did build the flare on the inside, so inside and out use a 1" 1/4 flare!!

[brucek]

I did build the flare on the inside, so inside and out use a 1" 1/4 flare!!

Aren't you adding length to the port with those flares and so lowering your tune?

Or did you calculate that into the original design.......

brucek

[collo]

Rodny Alvarez wrote:

I did build the flare on the inside, so inside and out use a 1" 1/4 flare!!

OK, that's great.

The voltage measurement is AC RMS, which is what you get with a multimeter on the AC volts setting.

It's OK to measure this at the amp.

When calculating the power, use the DC resistance seen by the amp. If the drivers are in series, this would be Re * 2, if they're in parallel it would be Re /2, (where Re is the value for one driver)

You would need to feed the sub a sine wave and slowly increase power until port noise is first detected, sitting close to the port.

I used the signal generator built into WinISD. You just have make sure you're getting a clean sine wave out of your PC

The frequencies I used in my testing were 20, 25, and 30 hz.
Since you mentioned that you heard some noise at 10hz, I would start there.

If you get a result, then move up in frequency by 5hz steps - ie 15, 20, 25, 30hz

Because of your low tune, as you move up in frequency, the port velocity will fall away. More power will be needed to get the velocity back up.

Also, port performance increases with frequency, requiring higher velocities for "chuffing", needing even more power.

Because of these two factors, you'll quickly get to the point where you can't add any more power. If you make 30hz, that would be fantastic, but I suspect that 20hz is about as far as you'll get!

regards
Collo

[SteveCallas]

I suspect his house will start complaining quite vocally before he can collect much useful data - it will be interesting to see how this turns out, good stuff

[Rodny Alvarez]

collo wrote:

When calculating the power, use the DC resistance seen by the amp. If the drivers are in series, this would be Re * 2, if they're in parallel it would be Re /2, (where Re is the value for one driver)

The subs are dual 4 ohm running in series to 8 ohms and then parallel to 4 ohm load.

I used the signal generator built into WinISD. You just have make sure you're
getting a clean sine wave out of your PC

Can I use the REW or I need WinSD??

[Rodny Alvarez]

brucek wrote:

Aren't you adding length to the port with those flares and so lowering your tune?

Or did you calculate that into the original design.......

brucek

I cut the port to 33", the original design was 35", I measure the port after installing the flares and they are 34.5", its pretty close, I dont think 1/2" will make a difference!

[collo]

Rodny Alvarez wrote:

The subs are dual 4 ohm running in series to 8 ohms and then parallel to 4 ohm load.

A little detective work.....
This shot from the Sound Splinter page for the RLP-15



For the Dual 4 ohm driver, it shows the Re as 6.1 ohms. This would be the total dc resistance with the voice coils in series. Since you are running a pair of these in parallel, the value we need for our calculations is 6.1 / 2 = 3.05 ohms

Can I use the REW or I need WinSD??

You can use the generator in REW

[brucek]

Just thinking out loud...

I know for the purpose of INPUT POWER, WINISD is using RMS E^2/Re, where they're assuming that at some point the complex impedance of the drivers will be their DCR, (and that would be the near maximum power, so it's a decent assumption), but I suspect Rodnys impedance will have a wild ride at those various frequencies if you examine the impedance curve of his LLT shown below.

Qty 2 SS D4 drivers
10" ID vent, 35" long, two flares.
38 cu. ft box
11.29Hz tune.....

I added an electronics 1st order rolloff at 10Hz for these - a standard assumption I suppose.

IMPEDANCE CURVE.
Minimum impedance at ~12Hz. That's where the highest AC current will be.




AIR VELOCITY
Shows maximum velocity at ~10.5 Hz. The highest chuffing possibility I suppose.
I used 2500 watts for Input Power for this graph.
I had to go to Input Power of ~630 watts to get the velocity down to 17m/sec (=5% - 340m/sec)



EXCURSION
Again I used 2500 watts input power for this diagram. Somewhat over spec for excursion, but I guess he'd never be applying this much power.




Since the EP2500 is likely in bridge mode, one channel will be inverted across its positive terminal, so you'll be measuring a double rail voltage between the speaker terminals.

I suspect that amplifier would realistically produce ~500 watts per channel into 8 ohms, so it would be using about +100 DC volt rails. RMS of that, less the drop across the output stage of the amp, would yield a maximum of about 64 AC volt RMS capability. So 64^2/8 = 515 watts. Seems about right.

So, you have the theoretical AC voltage of 64 + 64 across the two bridged positive terminals. But since it's in bridge mode they likely have reduced the rails a bit so not to fry the thing, but anyway, be aware and careful when you are measuring not the short anything out.......

I guess you'll only be turning it up to the point where it chuffs........

brucek

edit: changed voltage to impedance..... shouldn't write stuff at night......

[collo]

Hi Bruce,

I ran the idea of using the voltage measurement to determine input power past the WinISD people when I first started the experiments.

Janne replied... "Power means actually that sinusoidal RMS voltage of U=sqrt(Power*Re) is applied to the driver. This does not change with the impedance"

I seem to remember from my Electrical engineering days, that whilst impedence moves around with frequency, the power used remains resistive.


Looking at your estimate of velocity vs frequency, I would say we're probably only going to get a result for 10hz. I do have a range of figures in mind, but don't want to predudice any results by mentioning it just yet.